1. Field of the Invention
The present invention relates generally to solar heaters. More particularly, the present invention relates to thermosiphoning solar heaters with side mounted storage tanks.
2. Description of the Related Art
Solar heater systems are designed to capture heat from the sun and to store the solar heat until the heat is needed. In solar water heaters, the heat is ultimately transferred to water. Solar water heaters, which typically include a collector and storage tank, come in various forms including both active and passive systems.
In active systems, the collector is typically a flat plate collector, which includes a rectangle box, tubes that extend through the box and a transparent cover that covers the box. The tubes help capture heat and transfer the heat to water inside the tubes. A pump is used to circulate water from a storage tank through the collector and back to the storage tank (typically located in the house). The pump essentially pumps the hot water from the collector into the tank and the colder water out of the tank and into the collector. The pump is typically controlled by a control system that activates the pump when the temperature in the collector is higher than the temperature in the storage tank. The control system may also deactivate the pump when the temperature in the collector is lower than the temperature in the storage tank. In some cases, the storage tank may double as a hot water heater in order to back up the solar heating, i.e., it can heat the water when the temperature of the water in the collector is low. One advantage of active systems is that they provide better control of the system and therefore they can be operated more efficiently than other systems. Furthermore, using the control system, active systems can be configured to protect the collector from freezing in colder climates.
In passive systems, the heated water is moved via natural convection or city water pressure rather than using pumps. Although passive systems are generally less efficient than active systems, the passive approach is simple and economical. Compared to active systems, the passive system does not require controls, pumps, sensors or other mechanical components and therefore it is less expensive to operate and further it requires little or no maintenance over its lifetime. Passive systems come in various forms including batch and thermosiphon systems.
Batch systems such as breadbox solar water heaters or integrated collector storage systems are thought of as the simplest of all conventional solar water heaters. In batch systems, the storage tank is built into or integrated with the collector, i.e., a self contained system that serves as a solar collector and a storage tank. Batch systems typically consist of one or more storage tanks, which are disposed in an insulated enclosure having a transparent cover on one side. The side of the storage tanks facing the transparent cover is generally colored black to better absorb solar energy. Batch systems use water pressure from the city source (or well) to move water through the system. Each time a hot water tap is opened, heated water from the storage tank is delivered directly to the point of use or indirectly through an auxiliary tank (e.g., hot water heater). One advantage of batch systems is that the water does not have to be stored separately from the collector. Furthermore, due to the large mass storage, batch systems typically do not encounter freezing problems in colder climates.
Thermosiphon systems, on the other hand, include a flat plate collector and a separate storage tank. The flat plate collector may be similar to the flat plate collector used in the active system. However, unlike the active system, the storage tank is mounted above the collector to provide natural gravity flow of water, i.e., the heated water rises through the collector to the highest point in the system (e.g., top of storage tank) and the heavier cold water in the storage tank sinks to the lowest point in the system (e.g., bottom of collector) thereby displacing the lighter heated water. Most literature on the subject discusses placing the storage tank at least 18 inches above the collector in order to prevent reverse thermosiphoning at night when the temperatures are cooler.
Referring to FIG. 1, a thermosiphon system 10 will be described in greater detail. The thermosiphon system 10 includes a collector 12 and a storage tank 14 mounted above the collector 12. The collector 12 includes an inlet 16 at its lower end for receiving water from a lower portion of the storage tank 14 and an outlet 18 at its upper end for delivering heated water to an upper portion of the storage tank 14. As the sun shines on the collector 12, the water inside the collector 12 is heated. Due to natural convection, the heated water in the collector starts moving upwards. As it moves upwards, the heated water is moved to the top of the storage tank 14 and the colder water in the bottom of the storage tank 14 is moved to the bottom of the collector 12 thereby replacing the heated water that was moved upwards to the storage tank 14. Furthermore, the storage tank 14 typically includes an inlet 20 at the lower portion of the storage tank 14 and an outlet 22 at an upper portion of the storage tank 14. The inlet receives 20 water directly from a city water source (or well), and the outlet 22 delivers heated water to an auxiliary tank such as a hot water heater or point of use whenever the hot water tap is opened.
Unfortunately, thermosiphon systems such as these suffer from several drawbacks. For one, these systems can freeze in colder climates. The collector typically has low thermal mass especially when compared to the storage tank and therefore the liquid contained therein is susceptible to freezing. Counter measures such as drainage systems and heat exchangers typically must be implemented in order to correct the freezing problem. Unfortunately, these add complexity and cost to the system (which is supposed to be simple and economical). For another, most thermosiphon systems are bulky devices formed from large, awkward and heavy parts and therefore they are difficult to manage and install. This is especially true on roofs and for do it yourselfers with limited support. In some cases, due to the weight of the storage tank when filled, the roof underneath the storage tank must be made more structurally sound (e.g., the load of the storage tank is not evenly distributed). Furthermore, because these systems are large and heavy, the costs of shipping these products are exorbitantly high. In fact, in some cases, the cost of shipping may be higher than the cost of the product itself. Another drawback with thermosiphon systems is that they tend not to be aesthetically pleasing. While the collector typically follows the roof line, the storage tank does not and therefore it sticks out like a sore thumb, i.e., the storage tank protrudes higher than the collector. In some cases, this is the main reason people do not purchase thermosiphon systems.
Based on the foregoing, an improved solar heater and more particularly an improved thermosiphoning system is desired.